1. Field of the Invention
The present invention relates to primer for adhering an electroconductive metal oxide coating to a plastic substrate, to a method of making the primer, and to a method of adhering an electroconductive metal oxide coating to a plastic substrate.
2. Description of the Related Art
Plastic substrates encompass an important part of a vast variety of articles of manufacture. Such substrates include cast acrylics, stretched acrylics, polyurethane and polycarbonates, among others. Also included are laminates having one or more plastic outer surfaces, which laminates may include multiple layers of materials other than plastic, e.g. glass, laminated with plastic. Many applications require adhering a conductive metal oxide coating to the plastic surfaces for a variety of applications. For example, in the aircraft industry metal oxide coatings are bonded to plastic substrates to provide aircraft transparencies which are able, among other things, to melt ice and remove moisture from the aircraft transparency.
Efforts have been made to adhere various materials, including metals and metal oxides, to plastic surfaces.
U.S. Pat. No. 4,335,187 to Rukavina et al. discloses a metal retainer, e.g. a stainless steel retainer, for mounting an aircraft transparency to an aircraft body, which retainer is bonded to polycarbonate, e.g. the polycarbonate inboard ply of the transparency, by a polyurethane adhesive.
U.S. Pat. No. 4,435,450 to Coleman discloses applying abrasion resistant thin polyurethane coatings to polycarbonate based aircraft transparencies with crosslinked aliphatic polycarbonate urethane coatings applied from solutions of a prepolymer and a crosslinking agent which are flow or dip coated onto the substrate.
U.S. Pat. Nos. 4,554,318; 4,609,703 and 4,670,350 to Rukavina disclose copolymers of acrylic acid and cyanoethylacrylate for bonding indium oxide films to acrylic substrates. Also disclosed is a terpolymer of cyanoethylacrylate, acrylic acid and hydroxyethylacrylate for the same purpose.
U.S. Pat. No. 4,725,501 to Rukavina discloses a silicate/titanate copolymer for use as a primer to adhere a vinyl interlayer to stretched acrylic or indium/tin oxide coated stretched acrylic substrate.
Other combinations of metal oxides and methods for applying them to a substrate are described in U.S. Pat. Nos. 4,094,763; 4,113,599; 4,434,284; 4,610,771; 4,622,120; 4,904,526 and 5,178,966.
While various approaches and compositions to satisfactorily adhere a number of materials to plastic substrates are disclosed and are acceptable, there are limitations. More particularly, separation of the metal oxide coating from a substrate may be caused by poor adhesion and/or the stress of unequal expansion and contraction of the metal oxide coating with respect to the substrate. Even minor separation is generally undesirable for most applications.
As can be appreciated from the foregoing, it would be advantageous to provide a primer composition for promoting adhesion of a metal coating to a substrate that does not have the limitations of the presently available primers.